[SPARK-26708][SQL][FOLLOWUP] put the special handling of non-cascade …

…uncache in the uncache method

## What changes were proposed in this pull request?

This is a follow up of https://github.com/apache/spark/pull/23644/files , to make these methods less coupled with each other.

## How was this patch tested?

existing tests

Closes #23687 from cloud-fan/cache.

Authored-by: Wenchen Fan <wenchen@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/CacheManager.scala

@@ -160,46 +160,44 @@ class CacheManager extends Logging {
     }
     // Re-compile dependent cached queries after removing the cached query.
     if (!cascade) {
-      recacheByCondition(spark, _.find(_.sameResult(plan)).isDefined, clearCache = false)
+      recacheByCondition(spark, cd => {
+        // If the cache buffer has already been loaded, we don't need to recompile the cached plan,
+        // as it does not rely on the plan that has been uncached anymore, it will just produce
+        // data from the cache buffer.
+        // Note that the `CachedRDDBuilder.isCachedColumnBuffersLoaded` call is a non-locking
+        // status test and may not return the most accurate cache buffer state. So the worse case
+        // scenario can be:
+        // 1) The buffer has been loaded, but `isCachedColumnBuffersLoaded` returns false, then we
+        //    will clear the buffer and re-compiled the plan. It is inefficient but doesn't affect
+        //    correctness.
+        // 2) The buffer has been cleared, but `isCachedColumnBuffersLoaded` returns true, then we
+        //    will keep it as it is. It means the physical plan has been re-compiled already in the
+        //    other thread.
+        val cacheAlreadyLoaded = cd.cachedRepresentation.cacheBuilder.isCachedColumnBuffersLoaded
+        cd.plan.find(_.sameResult(plan)).isDefined && !cacheAlreadyLoaded
+      })
     }
   }
 
   /**
    * Tries to re-cache all the cache entries that refer to the given plan.
    */
   def recacheByPlan(spark: SparkSession, plan: LogicalPlan): Unit = {
-    recacheByCondition(spark, _.find(_.sameResult(plan)).isDefined)
+    recacheByCondition(spark, _.plan.find(_.sameResult(plan)).isDefined)
   }
 
+  /**
+   *  Re-caches all the cache entries that satisfies the given `condition`.
+   */
   private def recacheByCondition(
       spark: SparkSession,
-      condition: LogicalPlan => Boolean,
-      clearCache: Boolean = true): Unit = {
+      condition: CachedData => Boolean): Unit = {
     val needToRecache = scala.collection.mutable.ArrayBuffer.empty[CachedData]
     writeLock {
       val it = cachedData.iterator()
       while (it.hasNext) {
         val cd = it.next()
-        // If `clearCache` is false (which means the recache request comes from a non-cascading
-        // cache invalidation) and the cache buffer has already been loaded, we do not need to
-        // re-compile a physical plan because the old plan will not be used any more by the
-        // CacheManager although it still lives in compiled `Dataset`s and it could still work.
-        // Otherwise, it means either `clearCache` is true, then we have to clear the cache buffer
-        // and re-compile the physical plan; or it is a non-cascading cache invalidation and cache
-        // buffer is still empty, then we could have a more efficient new plan by removing
-        // dependency on the previously removed cache entries.
-        // Note that the `CachedRDDBuilder`.`isCachedColumnBuffersLoaded` call is a non-locking
-        // status test and may not return the most accurate cache buffer state. So the worse case
-        // scenario can be:
-        // 1) The buffer has been loaded, but `isCachedColumnBuffersLoaded` returns false, then we
-        //    will clear the buffer and build a new plan. It is inefficient but doesn't affect
-        //    correctness.
-        // 2) The buffer has been cleared, but `isCachedColumnBuffersLoaded` returns true, then we
-        //    will keep it as it is. It means the physical plan has been re-compiled already in the
-        //    other thread.
-        val buildNewPlan =
-          clearCache || !cd.cachedRepresentation.cacheBuilder.isCachedColumnBuffersLoaded
-        if (condition(cd.plan) && buildNewPlan) {
+        if (condition(cd)) {
           needToRecache += cd
           // Remove the cache entry before we create a new one, so that we can have a different
           // physical plan.
@@ -267,7 +265,7 @@ class CacheManager extends Logging {
       (fs, fs.makeQualified(path))
     }
 
-    recacheByCondition(spark, _.find(lookupAndRefresh(_, fs, qualifiedPath)).isDefined)
+    recacheByCondition(spark, _.plan.find(lookupAndRefresh(_, fs, qualifiedPath)).isDefined)
   }
 
   /**